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Record Details

On Use of Equivalent Building Dimensions in AERMOD - Alcoa
Record No: 11-VII-01      Last Update: 11/10/2011

EPA Region: 7     Fiscal Year: 2011
States: IA
Record Type: Action
Pollutants: PM     Sources: Aluminum Plant
Models: BPIP,AERMOD     Urban/Rural: Rural
Terrain: Low Terrain     Regulations: PSD
Guideline: Guideline     Database: Both
Oral/Written: Written     Involvement: Review and Comment
Subjects: Downwash
Fluid Modeling

Region VII requests review and concurrence from the Model
Clearinghouse regarding the use of fluid modeling studies to
develop "equivalent building dimension" (EBD) parameters to
replace building parameters generated by BPIPPRM for use in
the AERMOD air dispersion model specific to the Alcoa
Davenport Works facility.  Given the range of technical
changes in the AERMOD model generally, and specifically the
PRIME downwash algorithm in AERMOD, as compared to the ISC
model, we also believe that more studies and additional
guidance are needed before the EBD approach for determining
building parameters can be accepted for use in AERMOD

C/H Response:

We agree with the Region VII position to not approve the use
of EBD parameters in the particular case presented for the
Alcoa Davenport Works facility due to the technical issues
and concerns conveyed in the request memorandum, most
notably the inclusion of additional surface roughness
elements to account for the surface roughness of the actual
facility for the tests conducted to demonstrate the
equivalency of the EBDs.

Further, we also agree that additional technical challenges
with the EBD approach for determining alternative building
parameters have been introduced with the promulgation of the
AERMOD model, with PRIME downwash algorithms, replacing
ISCST3 as the preferred near-field dispersion model under
the EPA’s “Guideline on Air Quality Models,” published as
Appendix W to 40 CFR Part 51.  We feel that it is imperative
to reassess the past guidance and practices more broadly to
ensure that future studies provide a viable basis for
determining equivalent building parameters that are
appropriate for use with the AERMOD model.  Therefore
through this Model Clearinghouse response, all past EPA
guidance related to determining EBDs through wind tunnel
modeling (Ref: Record 94-IV-09) is hereby suspended until further
notice.  Please note that this should not be taken to 
imply that all such studies will be summarily rejected until 
the process of reassessing the guidance has been completed, 
but rather to indicate that any EBD studies being considered 
should be discussed with the appropriate reviewing authority 
as early in the process as possible and that the Model 
Clearinghouse should also be engaged as early as possible.
memo:  Review Results of Equivalent Building Dimensions
         for AERMOD
         Dated: 10/24/2011
         From:  George Bridgers, Model Clearinghouse Director
                  Air Quality Modeling Group, EPA
         To:    Michael Jay, Chief
                  Atmospheric Programs Section, Region 7
                Richard L. Daye, Regional Meteorologist
                  Atmospheric Programs Section, Region 7

Attachment A:  Alcoa Wind Study Report
         Dated: 1/09
         From:  CPP Inc., Wind Engineering and Air Quality Consultants
                  Ft. Collins, CO 80524
         To:    Alcoa Davenport Works, Bettendorf, IA

Attachment B:  Assessment_of_Alcoa_Davenport_Works_EBD_Study 

Letter:  Request to Review of Use of Equivalent Building Dimensions
           in AERMOD
         Dated: 6/23/11
         From:  Michael Jay, Chief
                  Atmospheric Programs Section, Region 7
         To:    George Bridgers, Model Clearinghouse Director
                  Air Quality Modeling Group, EPA

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